1. Field of the Invention
This invention relates to onboard tire inflation systems and, in particular, to onboard tire inflation systems having means for eliminating the need for manual valves at each of the tires and for extending rotary seal life.
2. Description of the Prior Art
The use of onboard tire inflation monitoring and/or tire inflation/deflation varying systems is known in the prior art, especially for use in heavy duty vehicles, such as military vehicles, wherein the vehicle will be travelling over a variety of terrains, such as over-the-road, off-the-road and/or desert conditions, and it is desirable to change the tire inflation pressure, especially of the driving wheels. Typically, such systems utilize a remote pressure gauge in the vehicle cab whereby the operator can monitor tire inflation and/or utilize a switch or control member whereby tire inflation can be varied from the cab, preferably on the move, according to the type of terrain the vehicle is presently traversing. It is known that superior vehicle performance can be obtained in over-the-road conditions with a relatively high tire pressure (i.e. for example 75-95 PSI), in off-highway conditions with a relatively lower tire pressure (i.e. for example about 40 PSI) and in desert conditions with a much lower tire pressure (i.e. for example about 8-15 PSI). An inherent difficulty with prior art vehicle onboard tire pressure inflation/deflation systems has been the need for providing reliable rotary seals to the wheel hub and tire assembly which is, of course, rotating relative to the vehicle. The prior art devices have usually utilized rifle drilled axle shafts and/or housings and/or rotary seals on the outboard ends of the wheel end assemblies or at other relatively unprotected areas on the wheel end. These prior art structures were not totally satisfactory as rifle drilling of the various axle components is an expensive and difficult operation and might tend to weaken the drilled component and as the rotary seals, which are usually not as robust as the other axle wheel end components, were mounted on the outboard ends or other relatively unprotected areas of the axles and thus subject to abuse and damage. Additionally, in the known prior art systems, individual manually operated valves were required at each wheel end and/or unbalanced pressure was maintained at the rotating seals which reduces seal life, and, if the seals wear, results in continuous leaking of the system.
An example of an improved axle wheel end assembly for an onboard tire inflation system utilizing rotary seals which are located in relatively well protected inboard locations may be seen by reference to copending U.S. Ser. No. 370,656, filed Apr. 21, 1982, and assigned to the assignee of this invention, now U.S. Pat. No. 4,434,833.